Electrolytic recording medium

ABSTRACT

AN IMPROVED, NMON-CATECHOL, ELECTROLYTIC RECORDING MEDIUM IS DISCLOSED COMPRISING A POROUS BASE SHEET IMPREGNATED WITH AN AQUEOUS MEDIUM, INCLUDING GALLIC ACID AS A MARKING INGREDIENT, AN ELECTROLYTE COMPRISING AN AMMONIUM CATION AND EITHER A CHLORIDE OR A NITRATE ANION, OR BOTH SPECIES, AND A WATER MISCIBLE SOLUBILIZER, SUCH AS A LOWER ALKANOL AND/OR A GLYCOL.

Aug. 29, 1972 A. s. DIAMOND E' 'AL 3,687,822

ELECTROLYTIC RECORDING MEDIUM Filed April 12, 1971 Y INVENTORS.

ARTHUR S. DIAMOND BY DAVID E. CARR ATTORNEYS.

M'WIMM United States Patent Ofice 3,687,822 ELECTROLYTIC RECORDING MEDIUM Arthur S. Diamond, Palos Verdes, and David E. Carr,

Playa Del Rey, Calif., assignors to Telantograph Corporation, Los Angeles, Calif.

Filed Apr. 12, 1971, Ser. No. 133,031 Int. Cl. B21h 1/20 U.S. Cl. 204-2 17 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to electrolytic recording media, and, more particularly, to an improved, wet, electrolytic recording paper for use with dissolving electrode type facsimile recording apparatus.

(2) Description of the prior art Recording paper of the wet electrolytic type is generally marked by passing the paper between a positive eroding metal anode electrode and a negative non-eroding cathode electrode. The paper is impregnated with an electrolytically conductive solution containing a marking ingredient, one or more electrolytes and various other stabilizing and image enhancing additives. When a voltage is applied between the electrodes, causing current to flow through the recording paper, metal ions dissolve at the anode, enter the wet paper and react with the marking ingredients of the impregnant to form a colored mark on the side of the paper in contact with the anode.

For facsimile recording purposes, a white paper is preferred; it should have the ability to produce marks having an optical density which bears a close linear relationship to the amount of current passed through the paper. The density of the mark area should be variable uniformly in a range from white for zero current flow through greys for current of intermediate magnitude to black for currents of maximum flow. A black mark is preferred to provide a good contrast with the white background.

There should also be a minimum of bleeding or fringing of the marks so as to provide good resolution. The unmarked paper while stored in a moist condition in sealed containers for extended periods of time prior to use, should remain stable without chemical decomposition of its ingredients which might cause discoloration of the paper or affect the reproducibility of results without recorder adjustment. Further, the marked paper should not become discolored, give oif unpleasant odors, release any substance to the environment, or transfer its mark to adjacent materials. The marked recording paper should be relatively insensitive to light even after repeated runs through any of the conventional copying machines involving exposure to ultraviolet or other strong light sources.

Most successful recording papers employ pyrocatechin, also called catechol, as the marking compound such as disclosed in U.S. Pat. No. 2,339,267, to J. V. L. Hogan et al. and U.S. Pat. No. 2,358,839, to E. R. Wagner. While catechol exhibits excellent marking properties with dissolving iron anode electrodes, it has many objectionable features. Catechol is a strong reducing agent; it is easily 3,687,822 Patented Aug. 29, 1972 oxidized whereupon it undergoes a color change from white to brown. Unlike most salts, catechol sublimes; when heated even moderately it passes directly from the solid to the vapor state. Thus, catechol is an extremely fugitive agent which permeates the air and redeposits on any exposed surface.

When catechol papers are recorded in quarters having inadequate ventilation, white Walls soon turn yellow as do papers, files, and clothing. Catechol vapors produce a black film on exposed metal surfaces. Paints which dry by air oxidation will not cure when freshly applied in an area containing catechol fumes. The paint remains pasty and soft to the touch. Even when dry, catechol papers stored in a file soon discolor adjacent records; the catechol vapor penetrates cardboard file jackets and other papers to discolor nearby documents.

Previous attempts to replace catechol have resulted in the development of silver marking papers which are in current use, but require an expensive printer blade. Other developments concern the use of modified polyhydric phenols, such as methylene disalicyclic acid (MDA), which is not as fugitive at catechol and which also marks with an iron blade. The serious objection to MDA is that it cannot produce a black image but yields a sepia colored mark.

SUMMARY OF THE INVENTION An improved electrolytic recording paper is provided in accordance with the invention by impregnating a porous paper sheet with an electrolytic recording solution containing gallic acid in combination with a water miscible solubilizer and an electrolyte combination which produces in solution an ammonium cation and either one or both of a chloride and a nitrate anion. The electrolytic recording paper in accordance with the invention provides good image density and full grey-scale reproduction but will not discolor or fade with age, will not discolor other documents when stored in a filing cabinet and will not transfer objectionable vapors or fumes to the environment.

These and many other attendant advantages of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a process for preparing an improved electrolytic recording medium in accordance with the invention;

FIG. 2 is a perspective view showing a small roll of electrolytic recording paper heat sealed in a moistureproof plastic bag; and

FIG. 3 is a schematic perspective view of a recording system in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a sheet 10 of high wet-strength, white paper or other porous base is fed from roll 12 and passes over turning roll 14 into the liquid electrolytic recording solution 16 contained within an impregnating tank 18. The web travels past submerged rolls 20 and 22 and absorbs the impregnating solution which distributes itself evenly throughout the sheet 10. The impregnated sheet 10 is turned by roll 24 and passes between pressure rollers 26 and 28 which adjust the water content in the sheet 10 to about 25 to 50% by weight on a wet basis. The impregnated sheet 10 is rewound on take-up roller 30. The sheet is then cut into smaller rolls 32 and is packaged and stored in a suitable, sealed container such as the heat sealed polyethylene bag 33 depicted in FIG. 2.

Referring now to FIG. '3, the impregnated sheet 10 is recorded by passing it between a stationary non-eroding anode 34 and a rotatable non-eroding cylindrical cathode 36 which has a prismatic helical electrode 38 wound around and projecting above its exterior surface. The electrode 38 sweeps a spot longitudinally across a knife-edge 40 of the eroding anode 34. Current passing between the anode 34 and the cathode 36 causes the anode to erode electrolytically and causes metal ions to enter the electrolytic solution with which sheet 10 has been impregnated. The ions are reduced to free metal by the marking ingredients and leave a dense black mark where the paper is contacted simultaneously on opposite sides by the anode and the cathode electrode, during the flow of electrical current.

The eroding anode electrode may be made of any suitable materials such as iron, stainless steel, or copper together with alloys of various metals as is well known in the art, but preferably is an alloy of iron, such as stainless steel. The cathode electrode may be made of any suitable, conductive metal capable of withstanding the abrasive effects of the moving recording paper. Metals found acceptable are platinum, platinum alloys, stainless steel and other materials well known in the art. The cathode is suitably formed of a platinum-iridium alloy.

Although gallic acid has been used in the past in combination with other marking compounds, it has never found acceptance as the single reactive marking ingredient component in a wet electrolytic recording paper. Mandel, US. 3,122,488 used gallic acid in conjunction with manganous chloride in an electrolytic recording medium of the non-eroding, or non-dissolving electrode type in which the impregnating solution is maintained at a relatively high pH value.

Gallic acid has limited solubility in aqueous solution and has been unacceptable in the past when used singly as a marking compound because of low image density and crystal formation on the electrodes during recording. Burning, i.e., the appearance of a yellow color in image areas on the front and/or back side of the sheet, is also experienced in recording with a conventional gallic acid formulation One aspect of the present invention relates to the use of a combination of a volatile and non-volatile aqueous solubilizer for the gallic acid. The volatile solubilizer can be a lower alcohol such as methanol, ethanol, propanol, or butanol. However, ethanol is preferred since methanol is toxic and propanol and butanol have rather unpleasant odors and therefore would be objectionable in confined areas.

Wet electrolytic sheets containing only ethanol as the solubilizer are found to dry too quickly on recording machines. Therefore, it is preferred to incorporate a nonvolatile solubilizer such as a polyhydric, aliphatic alcohol suitably glycerine, ethylene glycol, propylene glycol, and the like, in the formulation for the electrolytic recording medium. The glycols are non volatile and also function as humectants to maintain the optimum water level in the sheet and prevent salting out or crystal formation at the electrodes.

On a basis of 100 ml. of water, the formulation suitably contains from 100 to 400 ml. of alcohol and from about 20 to 150 ml. of polyhydric alcohol.

It has been discovered that a particular combination of ammonium, chloride, and nitrate ion species is needed to produce a dense black mark in a gallic acid containing electrolytic recording paper. More specifically, it has been found that the combination of ammonium and nitrate ions is optimum for electrolytic recording at low writing speeds, such as from to 50 inches per second, while the combination of ammonium and chloride ions is preferred at speeds above about 40 inches per second. Between these ranges, all three ions, when used in combination, give dense gray-black or neutral black, images.

It is not known how the ammonium cation, in conjunction with the chloride and nitrate anions, actually enhances the imaging capabilities of electrolytic recording paper impregnated with gallic acid. Alkali metal chlorides and nitrates have been used in the past to render the paper conductive but have not shown the profound effect on the marking compound discovered to take place betwefn ammonium chloride and nitrate salts and gallic 3C1 It might be postulated that ammoniacal solution is a more responsive alkaline precursor than sodium or potassium ions, in this system. Thus, under the action of electrical current flow ammoinum hydroxide may be rapidly generated thereby promoting the reaction between the iron stylus or printer blade and the gallic acid solution to form the intensely black iron gallate compound.

Alternately, it is possible that ammonium ions in solution increase either the speed with which the anode dissolves or the mobility of metal ions in solution, thereby making more iron available for the reaction to form iron gallate.

If only ammonium and chloride ions are used as the primary electrolytic species for low speed recording, insufiicient contrast is obtained. Highlight areas tend to print grey rather than remaining white and unmanked. It appears as though the paper is too sensitive to marking. The prints are flat and have a muddy appearance.

Also, chloride ion tends to impart a bluish cast to high density or black image areas when no nitrate ion is present or so little nitrate is incorporated as to be ineffective in modifying the color of the mark.

If, on the other hand, only ammonium and nitrate ions are used as the primary eelctrolytic species for high speed recording, low image density is obtained. The recording paper does not mark as easily.

Also the nitrate ion, at high recording speeds, tends to produce an overall brownish hue in image areas. The addition of chloride ion produces a more neutral black as it tends to shade the mark toward the blue end of the spectrum, but its presence is only necessary at the higher recording speeds, above about 40 inches per second.

In summary, for low speed recording, the combination of ammonium and nitrate ions is the preferred electrolyte; for high speed recording, the combination of ammonium and chloirde ions gives better print quality.

Any number of water-soluble ammonium compounds, such as ammonium acetate, chloride, citrate, formate, thiocyanate, nitrate, oxalate, and phosphate can be used alone or in combination to carry out the concept of this invention provided the pH of the final impregnating solution is maintained at a value of from 1.0 to about 4.0, preferably between 2.0 and 3.0; provided further that no metal ions such as iron, copper, chromium and titanium are introduced into the solution by the ammonium compound which might react with the marking compound to produce a colored metal lake; and, provided the quantity of ammonium compound employed is such that the impregnating solution contains from about 0.5 to 2.5 gram-ions of ammonium per liter, preferably from 0.5 to 1.5 gram-ions per liter. I

Likewise, any number of water soluble, alkali metal salts such as sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, and lithium chloride can be used alone or in combination to carry out the concept of this invention provided the optimum pH level is maintained; provided further that no reactive metal ions are introduced into solution which might cause a color reaction as previously mentioned; and futher provided that the total quantity of chloride and nitrate ions in solution is between 0.4 and 2.0 grams-ions per liter, preferably from 0.8 to 1.5 gram-ions per liter.

Other additives such as organic or inorganic acids may be provided to maintain a low pH between about 2.0 and 3.0 thereby preventing premature color formation. Suitable acids are at least one of phosphoric acid, oxalic acid, tannic acid and formic acid. The acids are suitably present in the medium in an amount below 10.0 grams per liter of solution and at a level necessary to achieve the desired pH.

Image tone can also be modified by including a minor amount of secondary marking ingredient such as catechol, methylene disalicylic acid (MDA), protocatechuic acid (PCA) dihydroxyphenylacetic acid (DHPAA), dihydroxy-phenyl-propionic acid (DHPPA) or any of the polyhydroxy phenolic marking ingredients disclosed in US. Pats. Nos. 3,344,043; 3,342,704; or 3,342,705. The ratio of gallic acid to secondary marking ingredient is preferably at least 3/1. The toal amount of marking ingredient is generally maintained between 20 and 100 grams and preferably between 30-50 grams per liter of solution.

The inclusion of an oxidizing agent such as taught in US. Pat. 2,953,505 to Mones speeds up the color-forming processes in the absence of heat and increases the sensitivity of the medium and provides greater marking density. Suitable oxidants are alkali metal chlorates, bromates, perchlorates, iodates and periodates. Suitably, sodium chlorate is present in the medium in an amount from 20 to 150 grams per liter of solution and the ratio of sodium chlorate to gallic acid is preferably from l/ 1 to 2/ 1.

Other ingredients such as thiourea, alkyl derivatives or thiourea or dithiobiuret may be present in small amounts, suitably below grams per liter of solution to stabilize the recorded mark.

The following examples are presented for purposes of specific illustration of the invention and are not intended to limit the scope of the invention.

EXAMPLE I A master batch of impregnant was formulated as follows:

The effect of electrolyte salt type on burning was investigated by adding the following salts to 300 ml. of the masterbatch as indicated in the following table.

TABLE I Amount, I Salt gm. pH Rate of solution Burning 20 2.6 Moderate Some. 20 S1 D0. 20 None 20 do Moderate.

150 ml. of additional water was added to the KC] sample to dissolve the KCl. The formulations were impregnated onto a sheet of paper and recorded in a conventional facsimile recorder with a stainless steel blade. The NH Cl formulation was the only paper exhibiting no burning. The lithium chloride paper was damp after recording and exhibited some background. The best copy was produced by the NH Cl containing sheet.

The effect of glycol level on heat aging properties was investigated as follows:

EXAMPLE 2 A masterbatch was prepared containing the following components:

Water to make 1500 ml.

300 ml. of portions of the masterbatch were combined with varying amounts of propylene glycol as follows:

TABLE II Amount, ml 0 3. 6 7. 0 14. 0 21. 0 pH 2. 1 2. 1 2. 1 2. 1 2. 1 Brightness, R 79.0 79.0 79.0 79.0 79. 0 Heat aged brightness, R42 79. 0 79. O 80. 0 79. 0 75.0

Propylene glycol does not alfect brightness of the recorded sheet at the levels tested, but does affect the brightness level after heat aging the sheet for 42 hours at F.

The optimum oxidant level is as established in the following experiments.

EXAMPLE 3 A masterbatch was prepared containing the following components:

Component: Amount Deionized water ml 1000 Thiourea gm 7.5 Formic acid ml 1.5 Sodium nitrate gm 2.50 Ammonium chloride gm 86.0 Sodium phosphate grn 1.6 Oxalic acid gm 2.4 Ethyl alcohol ml 325.0 Propylene glycol ml 40.0 Gallic acid gm 50.0

Water to make 1500 ml.

Varying amounts of sodium chlorate were added to 300 ml. portions of the masterbatch and impregnated into a paper base. The water content was adjusted to about 36% and the paper recorded on a facsimile machine to provide the following results:

TABLE III Amount of NaClOa,

Rat o NaClOs/gallie acid 0 0. 43/1 0. 86/1 1. 72/1 2.15/1 2. 5 2. 45 2. 3 2. 4 2. 3 Low Medium Good Excellent Good 84. 5 Medium Good Excellent Good 83. 5 82. 0 81. 0 79. 0 75. 0

The mark in each case was neutral black in color but best density was provided at a ratio of 1.72/1. Heat aging data indicates that all levels of chlorate utilized are acceptable but that a significant decrease in brightness is experienced at a chlorate to gallic acid ratio above 1.72/ 1.

It is to be understood that only preferred embodiments of the invention have been described and that numerous substitutions, modifications and alterations are all permissible without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

1. An electrolytic recording medium for marking a dissolving metal anode blade comprising a sheet impregnated with an aqueous electrolytically conducting marking solution containing:

gallic acid marking ingredient; and

a mixture of volatile and non-volatile aqueous miscible solubilizers.

2. A medium according to claim 1 in which said volatile solubilizer is a lower alkanol, said non-volatile solubilizer is a polyhydric alcohol and said solution contains on a basis of a liter of Water, 100 to 400 ml. of alkanol and 20 to 150 ml. of polyhydric alcohol.

3. A medium according to claim 2 in which said alkanol is ethanol and said polyhydric alcohol is a Watersoluble non-volatile glycol. l

4. A medium according to claim 3 in which the glycol is propylene glycol.

5. A medium according to claim 1 further including an electrolytic salt comprising an ammonium salt.

6. A medium according to claim 5 in which electrolytic salt comprises essentially a member selected from the group consisting of ammonium chloride, ammonium nitrate and mixtures thereof.

7. A medium according to claim 5 in which said electrolytic salt includes from about 0.5 to 2.5 grams-ions of ammonium per liter of said medium.

8. A medium according to claim 1 further including an oxidant salt.

9. A medium according to claim 8 in which the ratio by weight of gallic acid to oxidant salt is from 1:1 to 2:1.

10. A medium according to claim 8 in which the oxidant is an alkali metal chlorate.

11. A medium according to claim 1 in which the sheet contains from about 25 to 50% water.

12. A method of forming a mark on an electrolytic recording medium comprising the steps of:

impregnating an absorbent sheet with an aqueous solution containing gallic acid marking compound and a mixture of aqueous miscible volatile and nonvolatile solubilizers;

contacting a first surface of the sheet with a dissolving metal anode and the obverse surface with a non-dissolving cathode; and

passing current through said electrodes and sheet to dissolve and ionize said anode and react the ions with gallic acid to form a mark.

13. A method according to claim 12 in which said solution contains an electrolytic salt comprising an ammonium salt on the basis of about 0.5 to 2.5 gram-ions of ammonium per liter of solution and selected from the group consisting of ammonium chloride, ammonium nitrate and mixtures thereof.

14. A method according to claim 12 in which the water content of the sheet is adjusted to between 25 to by weight.

15. A method according to claim 12 in which the solution contains an oxidant salt and the ratio by weight of gallic acid to oxidant salt is from 1:1 to 2: 1.

16. A method according to claim 12 in which the volatile solubilizer is a lower alkanol and the non-volatile solubilizer is a polyhydric alcohol.

17. A method according to claim 16 in which the volatile solubilizer is ethanol and the non-volatile solubilizer is propylene glycol.

References Cited UNITED STATES PATENTS 2,953,505 9/1960 Mones 204-2 3,122,488 2/ 1964 Mandel 2042 3,122,489 2/1964 Mandel et a1 2042 3,123,542 3/1964 Mandel et 'al 204-2 GERALD L. KAPLAN, Primary Examiner T. TUFARIELLO, Assistant Examiner 

